1. Field of the Invention
The present invention relates generally to the field of prior art encompassing focusing mechanisms for optical instruments. More particularly, this invention relates to a coarse focus mechanism for use with microscopes or similar instruments.
2. Description of the Prior Art
Microscopes and related devices are precision optical instruments which basically include a heavy frame that is designed to be placed on a table top or other such level surface, cooperating lens and stage members supported on the frame, and a means for moving either the lens member or the stage member with respect to the other member for the purpose of focusing the specimen being viewed through the lens member. Like the frame, both the lens and stage members are generally precision made from heavy materials. When a focusing mechanism is utilized to support and move either of these members, it is critical that such a mechanism be capable of supporting the heavy movable member as well as providing precise degrees of movement in order to achieve the basic coarse focus of the specimen under study.
The prior art has recognized that the coarse focus of a microscope may be achieved by means of a simple rack and pinion gearing arrangement between the focusing mechanism and the movable member. Such focusing mechanisms may include a rotatable pinion shaft having a pinion gearing thereon for cooperative engagement with a rack carried by either the lens member or the stage member. By providing stop means at the opposite ends of the rack and utilizing a slip clutch drive for the knob which operates the pinion shaft, damage to the microscope can be avoided since manual operating force applied against the extreme ends of travel of the movable member can be controlled. The Fitzgibbons U.S. Pat. No. 3,451,739 is exemplary of this latter concept.
In utilizing slip clutch drives in conjunction with the coarse focus mechanism of a microscope, it is highly desirable that the manually operated knob for effecting the focus be accurately positioned on the pinion shaft in order that the slip clutch can be precisely adjusted to control and limit the amount of torque imparted to the shaft through the knob. It is further highly desirable that this positioning of the knob be achieved easily and quickly and also in such a manner as to facilitate the ultimate assembly and disassembly of the entire knob and slip clutch mechanism for servicing purposes.